This invention relates to an improved chuck for holding an electric motor armature for testing following its initial assembly.
In a typical armature test system, a conveyor moves assembled armatures to a testing station where the armatures are temporarily removed from the conveyor by means of a chuck. A motor armature includes a shaft and several coils of wire wrapped in slots formed between laminated iron and terminated by welding or staking in a commutator which includes contact bars.
One component of the chuck, a lower saddle, is attached to a pneumatic or hydraulic cylinder which is extended to lift the armatures off the conveyor and move them to a testing station where several electrical tests are performed. Another component of the chuck, the upper saddle, is associated with the testing station and includes a mechanism for positioning the armature as it is moved into position for testing.
The testing operation typically includes several tests, including: End-to-End Weld Test, which measures the electrical resistance of each wire-to-bar connection; Surge, where high voltage pulses are applied to individual coils and the resulting back-EMF ringing produced by the coils is measured as a function of time; Resistance, where the resistance of each coil in the armature is measured; and Hi-Pot, which is a test where high voltage is applied from the commutator to the grounded armature shaft.
Of particular concern in the present invention is the Surge test, which is a measure of the electrical inductance of each coil making up the tested armature. The use of a metal chuck to support the armature during testing adversely affects the quality of the surge or inductance test since the chuck becomes part of the magnetic path around each coil. Allowing the core of the armature to come into contact with a metal chuck attenuates the back-EMF ringing during the surge test. To overcome this problem, some prior art chucks have been made of stainless steel or Nylon.TM.. Stainless steel, although not as detrimental to the surge test as mild steel, nevertheless dampens or attenuates the ringing. Nylon, while non-magnetic and therefore ideal for its lack of detrimental effect on the surge test, tends to wear quickly due to the rotation of the armature relative to the chuck during the loading procedure.
Accordingly, it would be desirable to provide an armature testing chuck which is both non-magnetic and resistant to wear.